Environmentally Induced Sperm RNAs Transmit Cancer Susceptibility to Offspring in a Mouse Model

Abstract

BackgroundDNA sequence accounts for the majority of disease heritability, including cancer. However, it is becoming clear that environmentally-induced epigenetic inheritance can also occur. Epidemiological studies have shown that maternal exposure to the pesticide DDT in pregnancy is associated with increased breast cancer risk in women. Yet, the effects of paternal exposure to this and other pesticides on the progeny’s breast cancer development has not been investigated.MethodsMale mice (c57bl/6) were exposed to DDT or to a control-vehicle (CO) solution and used for sperm collection or mating with unexposed females to produce the DDT or CO daughters. In another experiment, normal mouse embryos (zygote stage) were injected with miRNA-10b and implanted into surrogate mothers to produce miR-10b offspring. DDT daughters or miRNA-10b females were used to study breast cancer development and metabolic parameters. Paternal sperm was used for RNA-seq analysis and miRNA expression levels.ResultsPre-conception paternal DDT exposure altered the sperm small non-coding RNA load, with an increase in miRNAs and a specific surge in miRNA-10b levels. DDT offspring weighed less at birth and at weaning, but became overweight and showed metabolic dysfunction in adulthood compared to CO. DDT daughters also showed increased mammary tumorigenesis, developing more aggressive tumors that grew faster than in CO. This tumor phenotype was linked to suppression of the AMPK energy sensing pathway and mTOR activation in mammary tissues. Remarkably, embryonic injection of miRNA-10b recapitulated the mammary gland and tumor phenotypes observed in DDT daughters.ConclusionsTo our knowledge, this is the first report of an association between paternal DDT exposure and breast cancer in offspring. Paternal DDT-induced programming of breast cancer development in daughters is mechanistically linked to sperm miRNA-10b. The impact of DDT and other endocrine disrupting chemicals on sperm and programming of breast and other cancers in offspring needs to be evaluated in humans.

Diet and Transgenerational Epigenetic Inheritance of Breast Cancer: The Role of the Paternal Germline

“…Moreover, the tumor phenotype was linked to regulation of the nutrient sensing mechanisms, with suppression of AMPK and increased mTOR activity in normal mammary tissues and tumors (40). Interestingly, another study from our lab showed that oral intake of the pesticide DDT in males also led to low birth weight and mammary tissue and tumor phenotypes, which were similar to those found for paternal malnutrition, including alterations in the energy sensing AMPK/mTOR axis, suggesting that there may be a common underlying mechanism for two distinct exposures (41). Paternally induced alterations in mitogenic pathways in daughter's mammary tissues are linked to epigenetic programing in DNA methylation and small non-coding RNAs such miRNAs and tRFs [ Table 1; (6,7,40)].…”

“…This will be a daunting task though, as population studies to identify epigenetic markers of ancestral exposure will likely take decades, given the temporal distance between the parental exposure and breast cancer onset in daughters. Another challenge to overcome and confirm findings from animal models in humans is the difficulty in ascertaining exposures in parents retrospectively, although data from our lab and others (40,41,55,61,72) suggest that different environmental insults alter the same non-coding RNAs in the male germline and could presumably be used as a marker of exposure if confirmed in humans. Studies on epigenetic inheritance of breast cancer in humans will also need to take into account the possible interaction between ancestral exposures with lifestyle and environmental factors after birth.…”

“…Interestingly, we also detected differences in sperm miRNAs when males were fed diets with two different types of fat (animal or vegetable origin) with a total of 89 miRNAs differentially expressed between the two groups ( 7 ). In more recent studies, we found that a low protein diet or oral consumption of the pesticide DDT altered the distribution and content of the major small RNA species detected, including microRNAs and tRFs in paternal sperm ( 40 , 41 ). More importantly, we showed that embryonic injections of miRNAs altered by those exposures can replicate the cancer phenotypes and play a functional role in the epigenetic transmission of breast cancer predisposition ( 41 ) as shown for other diseases ( 59 ).…”

“…Another possible strategy to reduce epigenetically induced predisposition to breast and other cancers in offspring would require interventions in the pre-conception window. Preliminary data from our lab and others suggest that environmentally induced effects on the male germline are transitory and can be reversed if the environmental insult is removed (41,84). Implementation of such measures in the human setting would require specific medical recommendations to men of reproductive age akin to those already in place for women undergoing pre-conception counseling.…”

“…Epigenetic information in sperm can be delivered to the oocyte during fertilization (55) and impact embryonic and fetal tissue development, including that of the mammary gland and alter breast cancer predisposition in offspring. Evidence in human and animal studies support the idea that epigenetic inheritance of breast cancer predisposition can be transmitted through the male germline(6,7,10,40,41,(56)(57)(58).…”